The present invention generally relates to the field of Electro-magnetic wave measurement and particularly to techniques for measuring a magnetic field of an integrated circuit (IC) inside the IC package, including the IC without the IC packaging. And more particularly to IC""s with densities about or greater than the current Large Scale Integrated (LSI) circuits.
FIG. 1 shows an example of a magnetic field distribution 114 of a package 110 having an integrated circuit (IC), for example, a LSI or an Ultra Large Scale integrated (ULSI) circuit. In FIG. 1 the package 110 is shown with cut-away section 112 illustrating the IC inside the package. Conventionally, the magnetic field distribution 114 outside of the package 110 is determined using a magnetic probe or sensor 116 from which induced voltage measurements are taken. In other words, typically measurements are taken of the IC outside of the IC packaging. The induced voltage is caused by currents in the integrated circuit and is used to determine the magnetic field at the position of the magnetic probe or sensor 116.
One reason for determining the magnetic field distribution of the package 110 is to solve any Electro-Magnetic Interference (EMI) problems that may be caused by the currents in the IC. In order to reduce the EMI, the source of the interference needs to be pinpointed. An example is given in Japanese Patent Application xe2x80x9cApparatus And The Method For Detecting Electromagnetic Wave Source, And Method For Analyzing The Same,xe2x80x9d by Uesaka Koichi, JP11-117028, filed Apr. 23, 1999. However, as circuit sizes shrink, for example, today LSI""s are produced by a 0.1 xcexcm process, it is necessary to perform measurements of the magnetic field very close to the circuit wirings, for example, cut-away section 112 inside the package 110, in order to pinpoint the source of potential interference.
In addition, determining the magnetic field distribution inside the IC package 110, may lead to production of low noise integrated circuits. Locations on the IC with a relatively high magnetic field indicate relatively high noise points. Of the several conventional techniques to reduce the magnetic field at these points, an example is changing the line pattern to reduce the noise.
Japanese Application No. JP11-006485, xe2x80x9cMethod And Apparatus For Measuring Electromagnetic Field Strength And Method And Apparatus For Measuring Current And Voltage Distribution,xe2x80x9d by Satoshi Kazama, et. al., filed Jan. 13, 1999, discloses the use of a loop antenna as a probe to determine the magnetic field over, for example, a circuit board. Other examples given are a lead wire of several centimeters, a microstrip line (i.e., a planar transmission line), a unit of a component on a board, and a circuit substrate of an electrical equipment. The loop probe is used for measurements in the neighborhood of 2 mm from the submitted equipment. Thus the disclosed use was for improving magnetic field determinations above equipment, for example, a unit on a board, not for inside an IC package.
In the above Japanese Application No. JP11-006485, the electromagnetic field of the circuit board generates an electric field coupling current and a magnetic field coupling current in a loop antenna above the circuit board. In the probe the electric field coupling current and the magnetic field coupling current are outputted toward the same direction at a certain part of the loop probe, but toward opposite directions at another part of the loop probe. A first composite current, i.e., electric field coupling current and the magnetic field, measured at one end of the loop probe by a current measuring device, gives the electric field coupling current plus the magnetic field coupling current. A second composite current measured at the same end of the loop probe by the same current measuring device, after rotating the loop probe 180 degrees, gives the electric field coupling current minus the magnetic field coupling current. Therefore, the electric field coupling current and the magnetic field coupling current can be calculated using these two composite currents. And the electric field component and the magnetic field component of the electromagnetic field at the loop probe can be derived from these composite currents.
However, using Japanese Application No. JP11-006485 in determining the magnetic field distribution of an IC package has only a secondary improvement in the measurement of the magnetic near-field distribution. Thus the conventional technique provides sufficiently accurate magnetic field measurements, and there is no significant advantage in using the techniques disclosed in Japanese Application No. JP11-006485 over the conventional techniques in the case of packaged IC magnetic field measurements. In addition, Japanese Application No. JP11-006485 rotates the probe to take the composite current measurements, when using one current measuring device. This rotation is time-consuming and a more efficient method of taking measurements is needed.
In order to pinpoint the source of potential interference in IC""s, measurements of the magnetic field on the order of tens of micrometers (xcexcm), for example, 30 xcexcm, above the IC wirings, i.e., inside the IC package, need to be made. Cut-away section 112 shows inside the IC package 110. However, in measuring the magnetic field inside the IC package, a significant coupling capacitance due to the electric field develops and the accuracy of the magnetic field probe to measure only the magnetic field deteriorates. Therefore there is need for techniques which minimize the effect of the electric field on the magnetic field probe inside an IC package to improve the accuracy of measurements of the magnetic field distribution.
The present invention provides a magnetic field measuring method and device for accurately determining the magnetic field distribution of an integrated circuit inside the IC package, including the IC without the IC packaging. In one embodiment, induced voltages due only to the magnetic field are determined at measurement heights on the order of 30 xcexcm, i.e., inside the IC package (or for example, the pre-packaged IC) by using a magnetic probe, having a loop of wire parallel to the current, for measuring the induced voltage of the horizontal component of the magnetic field. The induced voltage due to the electric field is removed by using a calculation including the difference of two measurements. The first measurement is taken with a voltage meter coupled to the first terminal of the loop of wire and ground coupled to the second terminal. And the second measurement has the couplings reversed due to a cross-bar switch, i.e., a voltage meter coupled to the second terminal of the loop of wire and ground coupled to the first terminal. Thus only the induced voltage due to the magnetic field remains, after the calculation. The magnetic field distribution for the integrated circuit may be determined by using the above procedure to scan a grid like pattern above the IC.
In another embodiment a method for determining a component of a magnetic field of an IC at a height above the IC on the same order of magnitude as a distance between the IC""s lines is provided. The method includes measuring a first induced voltage, having a first electric field induced voltage, due to a current carrying line""s electromagnetic field. A second induced voltage due to the current carrying line""s electromagnetic field is measured, such that the second induced voltage includes a second electric field voltage that is substantially equal to the first electric field induced voltage; The component of the magnetic field is determined based on a difference between the first induced voltage and the second induced voltage.
An alternate embodiment of the present invention provides a method for determining a magnetic field for a current carrying line of a plurality of current carrying lines inside an IC package, for example a LSI or VLSI circuit package. The method includes, measuring a first induced voltage due to a current carrying line""s electromagnetic field, where the first induced voltage has a first measured voltage proportional to a magnetic field produced by the current carrying line. Next, a second induced voltage due to said current carrying line""s electromagnetic field is measured in a manner so that the second induced voltage has a second voltage that is substantially equal to a negative of the magnitude of the first measured voltage; and a component or part of the magnetic field is determined based on a difference between the first induced voltage and the second induced voltage.
Another embodiment provides a magnetic field probe for determining a magnetic field distribution of a LSI circuit, including: a measuring probe for measuring an induced voltage produced by an electromagnetic field of the LSI circuit at a height above the integrated circuit on a same order of magnitude as a distance between the LSI""s circuit current carrying lines, the measuring probe including a first termination point coupled with a second termination point by an electronic circuit; a voltage measuring device for measuring the induced voltage; and a switch in which a first end is coupled to the measuring probe via the first and second termination points and a second end is coupled to the voltage measuring device and to ground, where when the switch is in a first position, the first termination point is coupled to the voltage measuring device and the second termination point is coupled to ground, and when the switch is in a second position, the first termination point is coupled to ground and the second termination point is coupled to the voltage measuring device.
These and other embodiments of the present invention are described in more detail in conjunction with the text below and attached figures.